The present invention relates to a rotary device for adjusting the position of a mechanism which requires a substantial degree of precision in calibration. The rotary adjustment device of the present invention is particularly applicable to the adjustment of a pivoted lever employed in the mechanism for actuating an electric switch; as, for example, the mechanism employed in a pressure switch of the type having a pressure sensing diaphragm movable to actuate a snap-acting electrical switch. In pressure switches of this latter type, typically employed for sensing the water level in a household washing machine, the diaphragm is preloaded by a suitable force-applying device. such as a compression spring which, in turn, has the length thereof adjustable by a lever mechanism for changing the preload of the spring on the diaphragm and thus the actuation point of the switch as desired for actuation at different preselected water levels. Switches of this type are typically employed to shut off the electrically operated water fill valve of the washing machine when the water level in the machine tub reaches the desired level.
Typically, in a household washing machine, the pressure switch employed for shutting off the electrically operated water fill valve or the washing machine tub has a control knob or lever extending from the machine control panel, enabling the machine operator to select the setting of the pressure switch for controlling the level of the water fill in the machine tub. The operator controlled knob or lever is typically directly connected to the internal lever mechanism of the pressure switch for changing the actuation point of the electrical switch therein. Appliance water level pressure switch applications of this sort typically employ a snap-acting switch which has a high degree of sensitivity to changes in the switch actuation point by an adjustment mechanism. Movement by an amount of only a very small fraction of an inch on the order of 1/32of an inch (0.8 mm) can result in a substantial change in the setting of the switch actuation point. Thus, inadvertent movement or undesired pressure on the selector lever or control knob after a selection of water level has been made can result in alteration of the setting of the pressure switch and an undesirable level of water flow. This problem has been particularly troublesome where the adjustment mechanism employed utilizes a rotary cam for adjusting the position of a lever mechanism such as is used in an appliance pressure switch.
It has thus been desired to find a way or means of desensitizing an adjustable pressure switch from inadvertent and undesired mechanical loading of the user movable control once the desired setting has been chosen. In particular, it has been desired to desensitize a pressure switch having a rotatable adjustment cam for selecting among various desired settings of the switch actuation point by changing the position of the adjustment cam with respect to the internal actuation mechanism for the switch.